cp's OEIS Frontend

A348586 Numbers k such that abs(A328258(k)) = abs(A328258(k+1)).

%I A348586 #11 Oct 24 2021 10:03:31
%S A348586 1,11,40,179,695,928,991,1079,2772,2799,2839,6687,7632,7739,7960,8568,
%T A348586 9347,10703,11008,11472,12847,12935,13580,14064,16000,16260,17135,
%U A348586 20944,26432,27999,35399,37236,42251,42756,44199,55308,56419,68976,70127,74671,77748,83099
%N A348586 Numbers k such that abs(A328258(k)) = abs(A328258(k+1)).
%C A348586 Equivalently, numbers k such that A328258(k) = -A328258(k+1).
%H A348586 Amiram Eldar, <a href="/A348586/b348586.txt">Table of n, a(n) for n = 1..1000</a>
%e A348586 1 is a term since abs(A328258(1)) = abs(A328258(2)) = 1.
%e A348586 11 is a term since abs(A328258(11)) = abs(A328258(12)) = 12.
%t A348586 f[p_, e_] := 1 - (-1)^p*(p^e); s[1] = 1; s[n_] := Abs[Times @@ (f @@@ FactorInteger[n])]; Select[Range[10^5], s[#] == s[# + 1] &]
%o A348586 (PARI) f(n) = sumdiv(n, d, if (gcd(d, n/d) == 1, (-1)^(d + 1) * d)); \\ A328258
%o A348586 isok(k) = f(k) + f(k+1) == 0; \\ _Michel Marcus_, Oct 24 2021
%Y A348586 The unitary version of A348585.
%Y A348586 Cf. A328258.
%Y A348586 Similar sequences: A002961, A064125, A206368, A333261.
%K A348586 nonn
%O A348586 1,2
%A A348586 _Amiram Eldar_, Oct 24 2021